This invention relates to a coaxial engine starter in which an operating rod of a solenoid switch and a motor rotor shaft are coaxially arranged.
FIG. 1 is a sectional view of a conventional engine starter, in which the engine starter comprises a front bracket 1 which serves as an outer housing of the starter with which the starter is mounted to an unillustrated engine. An output rotary shaft 2 is rotatably supported at its front end by a bearing 3 fitted in the front bracket 1. An over-running clutch 4 is axially slidably placed over the output rotary shaft 2. The over-running clutch 4 includes a clutch outer member 4a having splines 5 formed at its rear (left in FIG. 1) portion, a clutch inner member 4b having pinion 6 formed at its front (right in FIG. 1) and rollers disposed between the clutch outer 4a and the clutch inner 4b. A rotary shaft 7 of an electric motor has formed thereon a sun gear 7a of a planetary speed reduction gear which comprises an inner gear 8 and planetary gears 9.
The engine starter also comprises a solenoid switch 10 for controlling the electric current flowing into the starter and for moving forward the over-running clutch 4 through a pivotable lever 11. One end of the lever 11 is connected to a plunger 10a of the solenoid switch 10 and the other end is connected to the rear portion of the over-running clutch 4. A motor yoke 12 and a rear bracket 13 are securely connected to the front bracket 1 by bolts 14.
When an unillustrated ignition switch is turned on to start an engine, the solenoid switch 10 is closed and the motor rotor shaft 7 is rotated. The rotation of the shaft 7 is transmitted through the planetary speed reduction gear to the output rotary shaft 2 to drive the over-running clutch 4 which is connected to the output rotary shaft 2 through splines. Also, the lever 11 is pivotted by the forward movement of the plunger 10a of the solenoid switch 10 to move forward the over-running clutch 4. This causes the pinion 6 to engage the ring gear (not shown) of the engine so that the rotation of the shaft 7 is transmitted to the engine to start the engine. After the engine has been started, the rotation of the engine at a higher speed is transmitted to the pinion 6 through the ring gear. This rotational force of the pinion 6 is not transmitted to the motor shaft 7 due to the function of the over-running clutch 4 in which the backward transmission of the rotational force is prevented by the rollers 4c idling between the clutch outer member 4a and the clutch inner member 4b.
With the conventional engine starter as above described, the starter motor and the solenoid switch are arranged with their shafts in parallel to each other, so that a limitation is often imposed upon the engine layout. Further, several types of the front bracket must be designed separately for each model of the engine with the positions of the solenoid switch and the engine mounting opening of the front bracket taken into consideration. Therefore, the manufacturing cost is relatively high. Also, while the inner gear 8 is made by molding, the front bracket 1 is machined after die-casting, whereby the number of the manufacturing steps is large and the weight of the front bracket is heavy.